Brass retainer rings are currently fastened to artillery shells by spinning each shell at a high rate and then jamming the ring on it so that it is fastened or welded by friction between the two objects. This is an energy-inefficient process which heats and weakens more material that is desirable. The shell spinning at a high rate is also potentially dangerous.
Prior art laser welders which utilize an unstable optical cavity have an output beam wherein a far-field pattern is generated and is actually focused on the objects to be fastened. Thus, the weld occurs along the center-line or axis of the output beam and there is no hole in the center of the beam. Prior art welders of this type are limited to a few kilowatts (5-15 kw) of output power.